Maths!

philologos

maths maths maths maths
what do I have to learn for tomorrow

Irishstabber

the first 6 questions in paper 1

Strokesa

Yeah...what would be the best stuff to revise?

Irishstabber

Well I'll have my hands full with algebra algebra algebra...damn I HATE ALGEBRA :mad:

Mysteryfish

Really? I love algebra! It's completely pointless as i'm never going to use it later in life but its easy! What I hate is geometry! I can never work anything out. And no matter how hard I try my incircle nver touches all 3 sides. :-( Anyway, I'm just glad we have the weekend to study for paper 2.

As far as paper 1 goes, don't forget to revise tax and VAT and interest as sometimes, the simple questions have a twist in them that can throw you.

Irishstabber

Roll on Paper 2...Trigonometry, Geometry all my favourites

Mysteryfish

damn your mathamatical brain!

Strokesa

Thanks.
I really need to go study, yet im still here.
My stupidity ASTONISHES me, why have i no willpower?

Irishstabber

Mysteryfish wrote:

damn your mathamatical brain!

haha lmao I bloody wish :cool:
I just enjoy trigonometry, believe it or not...I love finding the angle degree of well angles in geometry.

Mimikyu

This post has been deleted.

Strokesa

Oh dear. I do honours and i cant do that...
How did u get x?

Hugh Hefner

I got x=2.84 and so on. Not 3. You just do a simultaneous equation. And then to find y just take one of the equations and substitute x for it's value.

Strokesa

Usually when i do simultaneous equations its all nice and straightforward with no decimals...i hate decimals they hurt my brain!

Mimikyu

This post has been deleted.

Hugh Hefner

Oh right sorry, I was being a complete idiot and was doing 2 x 9 = 19. *slaps self*

Strokesa

Bravo bravo. U should be in honours.
Or at least i should be in pass...

Mimikyu

This post has been deleted.

Flashling

Well, if all your working out is correct, the last bit definatly is, you're right.
For Math, learn line equations and laws of indicies, and theorums. Thats all really, though as Mysteryfish said maybe look over VAT? And BTW Mystery, algebra is great.

Mimikyu

This post has been deleted.

modular

The second part of the question is way easy.

You have x=3, so just substitute 3 for x in one of the original equations.

Take the first one: 2x-3y = 9

So:
2(3) - 3y = 9
6 - 3y = 9
-3y = -3

y = -1.

Mimikyu

This post has been deleted.

Hugh Hefner

modular wrote:

The second part of the question is way easy.

You have x=3, so just substitute 3 for x in one of the original equations.

Take the first one: 2x-3y = 9

So:
2(3) - 3y = 9
6 - 3y = 9
-3y = -3

y = -1.

Whoops a daisy. Looks like someone made a booboo. It's:-

2(3) - 3y = 9
6 - 3y = 9
-3y = 3
y = -1

modular

Hugh Hefner wrote:

Whoops a daisy. Looks like someone made a booboo. It's:-

2(3) - 3y = 9
6 - 3y = 9
-3y = 3
y = -1

That's one way of looking at it, yes.

You know what I meant.

Mysteryfish

Solitaryman666 wrote:

This post has been deleted.

Wait, isn't 4x-15x=-11x ? Or has my brain gone crazy? Am I missing something here?

modular

No, he's subtracting the lower from the upper, so is switching all the signs around.

Mysteryfish

but you add in simultaneous equations. hence the 57.
therefore, 4x+(-15x)=4x-15x=-11x

Fobia

Mysteryfish is right here, I was going to post but I didn't having said I wouldn't yesterday...

You add simultaneous equations, not subtract. If he had subtracted then he would have gotten 12y rather than 0y, a mistake many people make is using the term "cancelled", numbers don't magically vanish, there have to be none of them less, an idea is to write it out as 0y then simply take that out of the next line of your sum...

Back to the original question, one thing I notice is that Solitaryman666 wrote two different signs for the second equation in different posts, one must be right and one must be wrong...I havent time to figure out which is which atm so umm...good luck

modular

4x - 6y = 18
-15x - 6y = -39

He changes it mentally to:


4x - 6y = 18
15x + 6y = 39 (multiplied by -1)

---

19x = 57


so x = 3.

You can add OR subtract with simultaneous equations.

Mysteryfish

right so. I dunno, my brain is slowly desintegrating into nothing. I just got really confused for a moment. thanks for unconfusing me!

Nietzschean

there is quite a few ways of doing simultanious equations, it really depends what your given as to which is easier, i'm guessing the only 2 ways on the JC course would be substitiution and addition/subtraction as above.

In this case:
2x-3y = 9 (i)

5x+2y = 13 (ii)
Either would do, method one would give
x = (9 + 3y ) / 2 (iii)
which in eqn (ii) gives 5 ( (9+3y)/2) +2 y = 13
(multiply everything by 2 , and multiply in the 5 :
45 + 15 y + 4y = 26
19y = -19
y = -1
then putting this back in eqn (iii) gives x = 3.


The other as outlined before would be simplest by multiplying eqn (i) by 2 and (ii) by 3 and adding them,
one could also go 5 times (i) minus 2 times (ii).

Hugh Hefner

The way I do them is (using 666's example):-

2x-3y = 9 ===> 4x-6y = 18
5x+2y = 13===>+15x+6y = 39
......................19x+0y = 57
.......................x = 3


...................... 2(3)-3y = 9
.......................6-3y = 9
.......................-3y = 3
.......................y= -1



My way just seems less fiddly. Maybe I'm wrong. Anyway, the night before the Junior Cert. is probably not the best time to mention this.

Mimikyu

This post has been deleted.

Hugh Hefner

Solitaryman666 wrote:

This post has been deleted.

Eh, 2x-3y = 9 (to be mulitplied by 2) = 4x-6y = 18 not 4x+6y = 18.

You got it right cos' you kinda just added -15x and 4x and wrote 19x instead of -11x (the correct answer) and you added -39 and 18 and put down 57 whereas the actually answer for that would be -21.

Hugh Hefner resident party pooper.

Nietzschean

Hugh Hefner wrote:

The way I do them is (using 666's example):-
...

Well you could always use the matrix methods too its much clearer, but i doubt on the JC course..

Hugh Hefner

Darth Bobo wrote:

the matrix methods

I've not even heard of them.

Mysteryfish

the way hugh hefner did it is the way i woul, but there is so much confusion with all the methods...

Hugh Hefner

Are you talking about the higher level similtaneous equations question today? Cos' it messed up of me. I got the answers and then I tested if they would work in the other equation but they didn't. b was 5, I think, and c was -14 in one equation and 6/-6 in the other (I think ).

Mysteryfish

i can't remember what the answers were, but my sim. equa. all worked out for me in the exam. There was so many bloody surds 3rd roots that when i got to sim. equa. it was such a nice breather.

Big Ears

I did pass Maths , not that im not able for Hounours but because im too lazy to study enough for it . I beleive I got every question 100% right , so im on my way to an A .

philologos

Hugh Hefner wrote:

Are you talking about the higher level similtaneous equations question today? Cos' it messed up of me. I got the answers and then I tested if they would work in the other equation but they didn't. b was 5, I think, and c was -14 in one equation and 6/-6 in the other (I think ).

y was 14
x was 31
i think i might had got signs wrong

PurpleFistMixer

I got B as 6 and C as -5 if I can recall correctly.
There were a couple of simultaneous equations, though.

Flashling

b was 1 and c was -6. Worked out perfectly for me, but now you're making me doubt myself....

PurpleFistMixer

Okay just did it again a second ago and I got that.
I can't remember if I got the same in the exam though.... dayamn. Whatever it was I couldn't do the second part of that question anyway. Damn functions.

Fobia

There were simultaneous equations in that exam?!!1

That paper was alot harder than previous papers methinks, but I did alright, definitely a B...possibly an A, didn't manage to finish 2 C's so I hope the attempt marks will keep me up high..

One thing that my whole year didn't know was wtf a reciprocal was, apparently it's in the log tables but I didn't know and as such didn't bother to look (didn't open them the whole exam..), odd that they changed alot of the layout this year though. Alot more surds questions and several of those extremely annoying and hard "express my coffee in terms of x" questions.

Off to install my new Dvd-rw, screw irish paper 2

Furze

Anyone figure out Q. 3 (c) - the drinking choc question ?

Fenny

^ That turned out to be a quadratic equation, didn't it? I tried and I tried and I tried, but I kept getting x² + 30x + 108 = 0
(um, that's supposed to be a squared)
I could not for the life of me find factors for 108, so I just left it. The attempt marks shall keep me buoyed, and after talking to a few others, they seemed to get into that rut too - though someone said it worked out and they had 150, so I'm not sure what the right answer is.

modular

Furze wrote:

Anyone figure out Q. 3 (c) - the drinking choc question ?

I got 90g @ 4c per gram in normal time.
120g @ 3c per gram in promotion time.

PurpleFistMixer

Holy christ you almost gave me a heartattack there modular. I only found out how many grammes there were (got the same figures though). Checked the papers. Didn't have to find out how much it was per gram. Phew.

And I couldn't have been bothered to find the factors for it, so I just used the quadratic formula. Heh, whenever I got stuck in that exam I just started using that formula. Even in the functions questions...

There is a section on recipricols in the log tables (I was finished, started reading log tables to try learn some Irish) but it's for logarithms and doesn't actually say anything helpful about what recipricols actually are.

modular

I managed to use the log tables to help me in the reciprocal question. I thought it might have been the fraction upside-down, so when I looked up the reciprocal of 35, and it looked like 2/7 in decimals, I pretty much knew I was right.

Furze

modular wrote:

I got 90g @ 4c per gram in normal time.
120g @ 3c per gram in promotion time.

Fenny,
Did the exact same, maybe my scribbles will count for something !

Modular,
If u get a spare couple of hours; can you post the solution ?

Hugh Hefner

Oh God! I got like 11100 grams! The more I think about that test the worse I think I did. Boohoohoo! I'm seriously worried about my A now!